1. Field of the Invention
This invention relates to methods of making leak-tight joints in tube and shell heat exchangers, and particularly to methods applicable to non-brazed heat exchangers.
2. Description of the Prior Art
The invention may be regarded as an improvement upon prior U.S. Pat. No. 4,152,818, issued May 8, 1979 to Charles B. Mort, et al and entitled Making Mechanical Tube Joints. Problems inhering in attempting to make leak-tight joints in non-brazed heat exchangers are explained in that patent, and solutions therefor disclosed. In a preferred solution, according to the patent, a rivet-like member, termed a ferrule, is inserted in a tube end and is deformed radially to expand the tube end into contact with the peripheral wall surface of a hole in a header in which the tube end is received. As brought out in the patent, this step is itself insufficient to establish integrity of the tube-header joints, especially under circumstances in which even minor leaks cannot be tolerated. Accordingly, in the patent, the first metal working step is followed by a second metal working step, the two steps being carried out in the course of oppositely directed generally axial thrusts and over specified distances. The second metal working step, while it insures leak-tight joints in the assembled heat exchanger, is an additional process step and adds to production costs. Consideration of ways in which this added step might be omitted, without jeopardizing integrity of the tube-header joints, has led to the present invention.
The foregoing discussion embodies a disclosure of all of the prior art of which we are aware, material to the question of patentability of the invention, and is intended as compliance with revised Section 1.97 of Title 37 of the Code of Federal Regulations.